The Light Shield (LS) or Aperture Grid is a critical structural component in back-illuminated complementary metal-oxide-semiconductor (BSI CMOS) image sensors, designed to suppress optical crosstalk and precisely define the pixel's optical aperture T1 A2.In the LS_GRID module, after the sequential deposition of the barrier, the main light-blocking metal (typically W), and the Oxide Grid Seal Layer, the wafer must undergo a Pre Litho Cleaning step prior to photoresist application A1.This specific